* Tens of thousands unaccounted for

* First deaths confirmed in epicentre Wenchuan

* More than 18,000 buried in city of Mianyang, Sichuan

* Confirmed deaths in Mianzhu, Sichuan, rise to 3,000

(Adds fresh details and official quotes in paragraphs 9-12, 15-18)

By Ben Blanchard

DUJIANGYAN, China, May 13 (Reuters) - The death toll in China's earthquake climbed past 13,000 on Tuesday and looked likely to rise much higher after media said some 19,000 people were buried in rubble in just one area.

Rain and severed roads hampered rescuers in the mountainous area near the epicentre of Monday's 7.9-magnitude quake in the southwestern province of Sichuan, China's worst earthquake in over three decades.

State media reported devastation as troops reached stricken villages near the epicentre in Wenchuan, a remote county cut off by landslides about 100 km (60 miles) northwest of the provincial capital, Chengdu.

Officials announced late on Tuesday that 500 Wenchuan residents were confirmed dead, the Xinhua news agency reported. But the toll there and elsewhere is likely to soar.

Thirty People's Liberation Army (PLA) troops arrived at Wenchuan's Yingxiu township and rescued 300 residents, Xinhua said. But only 2,000 were found alive in the town of 12,000, according to a local official.

"They could hear people under the debris calling for help but no one could, because there were no professional rescue teams," state television quoted the official He Biao as saying.

About 60,000 people were unaccounted for across Wenchuan.

"What we most need is medicine. There is no medicine, there are no doctors and after such a long time, no food," He said.

Attempts to find survivors have become a race against time and bad weather. Premier Wen Jiabao, who has thrown himself into the task of running these efforts, told officials not to slacken.

"The disaster situation is worse than expected, and the rescue sites are quite complex," Wen said, according to Xinhua.

He ordered 3,000 medical staff to travel to Sichuan.

But official reports have presented a grim litany of rising death, suggesting that crumpled homes, schools and factories will yield many more bodies than survivors.

In Mianzhu, Sichuan, rescuers said the death toll had risen to 3,000. About 500 people were pulled out alive from crushed buildings. An earlier report said 10,000 people there had been buried under rubble.

A further 18,645 people were buried under debris in Mianyang, a city that also covers much farmland, Xinhua said.

In hard-hit Beichuan County in Mianyang, at least 1,000 students and teachers were buried under a seven-storey school building, and rows of apartment buildings in the town collapsed.

Locals told Xinhua that up to 8,000 residents may have died.

"People escaped from the buildings but were only devoured by the landslides," one survivor, Lei Xiaoying, told Xinhua. "There was no way to escape."

Over 320 deaths from the quake have so far been confirmed in provinces apart from Sichuan.

"NOTHING TO EAT"

Officials have said more powerful aftershocks could hit the region and mudslides may add to the toll.

A strong aftershock rocked Chengdu on Tuesday, one of 2,354 in the province over the past day that have unnerved residents and led many to sleep outside.

More than 50,000 troops joined disaster relief efforts or were advancing to the area. The Chinese air force said 6,500 troops were parachuted into hard-hit areas where rain and clouds had prevented military helicopters from landing.

"Please speed up the shipping of food. The kids have nothing to eat now," Wen said amid crying children.

In Dujiangyan, about midway between Chengdu and the epicentre, bodies lined streets and residents cradled possessions in front of homes reduced to piles of rubble.

Rescuers worked through the night, pulling bodies from ruined buildings after the earthquake, which rolled from Sichuan across China and was felt as far away as Bangkok and Hanoi.

About 900 teenagers were buried under a collapsed three-storey school building. Frantic relatives tried to push past a line of soldiers, desperate for news of their children.

"We're still pulling out people alive, but many, many have died," said one medical worker.

A group of 31 British tourists visiting the Wolong panda reserve in the quake-hit area have returned safe and uninjured to the provincial capital, China's Foreign Ministry said.

China said that there had been no reports of foreign casualties by midday (0400 GMT).

The quake was the worst to hit China since the 1976 Tangshan tremor in northeastern China where up to 300,000 died.

Analysts said they did not expect serious economic effects from the disaster but supply shortages could fuel inflation, already at a near 12-year high.

The State Administration of Grain ordered local governments to ensure grain and cooking oil supplies and price stability.

Offers of aid have come from all over the world, three months before the Beijing Olympics.

Olympic officials assured foreigners China was safe. A minute's silence will start each stop of the domestic torch relay and celebrations will be scaled down. (Writing by Chris Buckley; Editing by Nick Macfie and Charles Dick)

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